Mixed phase, alpha-beta titanium base alloys



Sept. 29, 1964 M. B. voRDAHl. 3,151,003

MIXED PHASE, ALPHA-BETA TITANIUM BASE ALLoYs Filed Feb. 1s, 1961 5sheets-sheet z IE7-i ULT/MAT: sreEwa-r-H vs. ELoNGAr/on Fae 77- 7 MNA/.Lag auE/vcmso FRoM ez/ ow BE7-A Tenn/.sus Alva Asso Ar VAR/ousrEMPceATu/ess A/vo r/Mrs 65910 roe PLcrs.' .S'oL/o oor.:- ns WATER'QuE/verven C feci. 5 "As wa Tse QuE/VCHED ANO Ariza zoo o D Y E 0. 18o Q0)" lk 160 h 0 V) ,/go/ 3 O 5 IO 15 20 25 30 ELo/vGAr/o/v, 17IN l 'lINVENTOR. Mura/v5 WnQDaHL.

ATTORNEKS'.

ULT/MATE STRENGTH, 1000 Ps1 Sept. 29, 1964 M a VORDAHL 3,151,003

MIXED PHASE, ALPHA-'BETA TITANIUM BASE ALLOYS Filed Feb. 13. 1961 5Sheets-Sheet 3 ULTIMATE STRENGTH VJ'- ELONG'ATION FUR VAR/GUS MIXEDPHASE, ALPHA-BETA TITANIUM 8445 LLQYJ AS QUENCHED FROM ASGI/E BETATRANJUS TEMPERATURE HND THEREAFTEB 465D BELOW `$5771 TRNSUS ELo/vGAr/olv1N VEN TOR. f/Lro/VB Vines/VH1..

ATTORNEYS.

5 Sheets-Sheet 4 M. B. VORDAHL MIXED PHASE, ALFHA-BETA TITANIUM BASEALLOYS ULT/MATE STRENGTH v5. ELoNGAr/o/v Foe VAR/ous MIXED PHASE,ALPHA-'BETA- TlTAN/UM BASEALLOYJ A5 GUENCHED FROM BELOW BETA TPANSUSTEMPERATUE AND THERAF'TEE AG'E'D.`-

Sept. 29, 1964 Filed Feb. 13. 1961 INVENTOR. /L TONE. I@ @of/HL A rToRNEYS.

15 Z0 ELO NGA r/o/v Z IOO Sept- 29, 1954 M. B. voRDAHL 3,151,003

MIXED PHASE, ALPHA-BETA TITANIUM BASE ALLOYS Filed Feb. 13. 1961 5Sheets-She@` 5 BETA TRANSUS TEMPERATURE YS. ALLOY CONTENT mi? VARIOUSTITANIUM BASE BIA/ART ALLOY SYSTEMS FCR E 10o F'M" 0 5 t0 I5 2O 25 30WEIGHT PERCENT ALLor INVENTOR. /W/Lro/VB. QPDA'HL.

BY MMMMMMM l T TORNE V5.

United States A Patent O 3,151,003 l lVmED PHASE, ALPHA-BETA TITANIUMBASE ALLOYS Milton B. Vordahl, Beaver, Pa., assigner to Crucible SteelCompany of America, Pittsburgh, Pa., a corporation of New Jersey FiledFeb. 13, 1961, Ser. No. 88,943 5 Claims. (Cl. 14S-32.5)

This invention pertains to methods of heat treating titanium base alloyshaving a mixed alpha-beta microstructure for imparting theretoexceptionally high strength and thermal stability, combined withadequate ductility for purposes of fabrication and for use underconditions of service. The invention also pertains to the resulting heattreated alloys.

This application is a continuation-in-part of my copending applicationSerial No. 435,754, led June 10, 1954 (now Patent No. 2,974,076, issuedMarch 7, 1961), which is in turn a continuation-in-part of myapplications Serial No. 132,327, tiled December 10, 1949 (nowabandoned); Serial No. 229,143, tiled May 13, 1951) now Patent No.2,950,191, issued August 23, 1960); Serial No. 424,569, filed April 21,1954 (now Patent No. 2,950,192, issued August 23, 1960); Serial No.323,155, filed November 28, 1952 (now abandoned), and Serial No.671,316, filed July l1, 1957 (now Patent No. 2,857,269).

In the rst three of my above-mentioned applications referred to, I havedescribed methods for imparting to titanium base alloys having a mixedalpha-beta microstructure, optimum combinations of strength andductility, and high ductility at any given strength level, said methodsconsisting essentially in subjecting such alloys to prolonged plasticdeformation at temperature within the mixed alpha-beta temperaturerange, i.e., at temperature below the beta transus temperature at whichthe microstructure of these alloys converts from mixed alpha-beta toall-beta on heating. As set forth in said applications, the preferredtemperature range for carrying out said plastic deformation `extendsfrom about 400 C. or 750 F. up to not more than about 50 C. or 100 F.below the beta transus temperature.

As shown in said applications, the effect of plastically deforming suchmixed phase alloys within the two phase temperature field, is to impartthereto a microstructure comprising a coherent admixture or interleaveddispersion of small bodies of alpha titanium and of beta titanium. Sincethe alpha phase of titanium is relatively weak and ductile, while thebeta phase is relatively strong but less ductile, the result of thisinterleaving and dispersion of the two phase is to impart uniformlythroughout the alloy a combination of high strength and high ductility.

The field of utility of the processes described in said application is,however, restricted to conditions of fabrication wherein the alloys canbe plastically deformed to the extent required for imparting theaforesaid microstructure, such, for example, as rolling into sheet orrod or drawing into wire, etc. Where, however, such alloys must befabricated into relatively large forgings, they cannot in many instancesbe worked or plastically deformed suiiiciently in the two phase field tosecure the full benets of the processes described in said application.Accordingly, a primary object of the present invention is to providemethods of so heat treating such alloys as to duplicate or surpass thestrength and ductility properties impartable thereto by the two phasefield, plastic deformation procedures of my earlier applications abovementioned.

Basically the heat treating processes of the present inventionapplicable to titanium base alloys having a mixed alpha-betamicrostructure, consists in quenching such alloys from a temperaturesubstantially below, i.e., at least `assumes an all-beta microstructure.from above to below the beta transus temperature, pre- ICC 50-l00 F.-below, the beta transus temperature of the alloy, and thereuponsubjecting the alloy to an aging treatment and preferably to a prolongedaging heat treatment at a somewhat lower temperature. Broadly stated,the quenching temperature range will extend from about 50 F. below thebeta transus temperature down to about 400 F. below the beta transus, amore preferred range extending from about 150 to 300 F. below the betatransus temperature, but in no instance is the quenching carried out ata temperature below about 1100" F. The subsequent aging treatment iscarried out within a ternperature rangetbroadly stated of about 750-1000F. for a period of about 1 to 50 hours, a more preferred aging procedurebeing to age the alloys after quenching, within the `temperature rangeof about G-900 F. for a period of about 2 to 12 hours.

In order to render the sub-critical temperature quenching treatment ofthe invention most eective in strengthening the alloy, the heattreatment must consist in two main steps, first obtaining a gooddistribution or interdispersion of the alpha and beta phases, andsecondly quenching in such manner as not to destroy the good alpha tobeta distribution obtained by the preceding step.

The first step can, of course, be carried out by the procedure outlinedin my above mentioned earlier applications, i.e., by plastic deformationof the alloy at temperature within the two phase field. Particularlygood dispersions are thus obtained with the alpha and beta `particleselongated and interleaved as results, for example,

by rolling or drawing, since this `results in greater strength in thedirection of the applied stress.

An advantage of securing a good dispersion of the alpha and beta phasesby plastic deformation in the two phasel crease the ductility at a givenstrength level and this effect is quite independent of4 the priorhistory or prior heat treatment of the alloy. Whether the alloy has beenhardened by quenching from the beta eld or from a lower temperature, orhas been previously fully annealed, as by slow or furnace cooling from abeta field temperature, or given any other treatment, extensive workingin the two phase field still develops the optimum properties, i.e., thehighest ductility at a given strength level.

However, it is not always possible to subject the alloy to such plasticdeformation in the two phase field prior to subjecting the same to thequench hardening heat treatment of the present invention. A good exampleof this is the case of massive forgings requiring Working in the betatemperature field, in which case an acceptable alternative for securinga good alpha to beta distribution, is obtained by slow cooling fromabove the beta transus temperature,` i.e., from a temperature at whichthe alloy Such slow cooling cipitating the alpha phase by a processwhich may be termed solid state dendritic growth, more commonly known asa Widmanstaetten structure, to give a resulting microstructure which isgenerally lamellar in character.

The conventional practice for quench hardening alloys in general is toquench from above the critical temperature at which the alloy assumes asingle phase microstructure. Thus, in the case of hardenable andtemperable, martensitc steel, quench hardening is effected by quenchingfrom the austenitizing temperature range,` i.e., from above thetemperature at which the steel converts from ferrite to austenite onheating. Depending on the rate of quenching and on the carbon contentand the contents of other -alloying elements present, any desired`degree of hardening, within limits, may be thus obtained,

yThe `data in following quenching. Such heat treatment is desirable,because of the ease with which Vit may be conducted.

with accompanying increase in ductility by subsequent tempering at asubcriti'c'al temperature.

-In the case `of the mixed-phase alpha-beta titanium base alloys,however, quenching from above the lbeta transus temperature results ingeneral in an extremely brittle alloy which .cannotthereafter betransformed into a strong and ductile alloy by subsequent heat treatmentat a temperature below the beta transus temperature.

In contrast, however, and by employment of the process of the presentinvention, wherein the alloy has' rst imparted thereto a good alpha-betaldistribution as by plastic deformation, inthe lalpha-beta eld, or byslow cooling from the all-beta held, and thereafter quenching from atemperature below the beta transus temperature, there is imparted to thealloy an excellent combination of strength and ductility, all `assubstantiated by the comparative test datarhereinafter presented.

Applicant is aware of no other instance in metallurgy wherein it hasbeen established as optimum to initiate hardening by quenchingmfromrwithin `a two phase field rather than from a higher temperature singlephase field; or wherein prior to quenching from within a two phase ield,the two phases ofthe alloy are advantageously distributed, by either ofthe two procedures aforesaid, i.e., by prior plastic deformation in thetwo phase field, or by slow cooling -from a higher temperature singlephase field.

`The 'following Table I shows the effect on ultimate strength andtensile elongation of heat treating various mixed `alpha-beta titaniumbase alloys by (a) quenching from above the beta transus temperaturefollowed by aging or tempering at a temperature below the beta transus',and (b) quenching from below the beta transus temperature followed bytempering or aging at a still lower temperature. Y

TABLE I Composition Elong. percent Treatment Ultimate pertalance (psi.)cent Titanium) (a) Mo 1,000? C. min. quenched into 161, 900 0 water;tempered 800 F. for 10 min. (a) 6Mo --d0- 188, 800 2 (b)6Mo 850" C. 15min. quenched into 189, 200 4 water; tempered 800F. for 10 190, 800 4min. (a) 6Mo-0.1N' Quenehed into water` 10 min. 191,700 0 900 C.;tempered 20 min. 575 184, 000 2 C. 191,300 2 192,200 2 (b) GMO-01N-.Quenched into water 10 min. 191,700 3 850 C.; tempered 20 min. 575195,000 4 C. r 197, 800 2 198, 800 3 (a) 4Mn Quenehed into water 15 min.174,800 1 1,000 C.; tempered 20 min.- 173,900 0 550 C. 181,100 0 l 177,300 2 (b) 4Mn Cold rolled; quenched intowater 175, 200 6 for 15 min. 725C.; tempered 177,300 5 for min. 450 C. 173, 700 5 173, 100 2 It will beseen Vfrom the' above table that in each instance where the specimen wasquenched from above the beta transus temperature and thereafter temperedbelow Table I are based Aon short time tempering Furthermore, itjresultsin an ideal microstructure Iin that the'distribution'of'the two phases,ie., alpha andb'e'ta, is ideal vasrfar fas strength and ductility areconcerned.y The microstructure consists of a beta phase matrix whichcontains airandomdstribution of globular alpha phase islands. NoV betterdistribution with respect to ductility is conceivable. The objection tothis short VItime 'tempering treatment following tempering, however, isthat it is not thermally stable. On long time exposure to moderatelyelevated temperatures, transformation takes place, due to furtherconversion of the retained beta into the alpha phase, so that themechanical properties are consequently altered resulting in ia decreasein ductility. Hence the material in `this condition is not suitable forapplications where elevated temperature service is encountered.

For imparting thermal stability, the mixed phase alloys as quenched fromthe alpha-beta field are, in accordance with a further aspect of theinvention, subjected to an aging heat treatment in the temperature rangeof about 750-1000 F. and preferably, for optimum results', at about800-900 F. Although relatively short time aging upto about 1 hour or sosubstantially increases the thermal stability as compared to the asquenched condition, for imparting maximum thermal stability, prolongedaging or overaging is required. Thus, duration `of the aging cycle mayvary over a broad range of about 1 to 50 hours, a preferred aging cyclefor good thermal stability being from 2 to 12 hours.

The data contained in the following Table II is illustrative of thevresults obtainable by application of the aforesaid heat treatmentaccording to the invention, to a typical mixed phase, alpha-betatitanium base alloy containing about `6.5% y'manganese and the balancetitanium of commerical purity. An ingot of this alloy as produced byvarc melting in a cold mold furnace in an inert or argon atmosphere, washot rolled at l300 F. and a series of test specirnensprep'aredtherefrom. Groups of these specimens were then heated for 2 hours at1109" to 1500" in an inert atmosphere, and quenched in water to roomtemperature. Individual specimens were then aged at temperatures' of700-1090o F. for the periods indicated in the table, and 'tested forroom temperature mechanical properties with results as set forth.

TABLE II Quenched and Aged Tensile Propertzes on T1-,6.5 Mn AlloyTensile Properties Aging Aging Water Quench Temp., Time,

Time and Temp. F. hrs. Ult. 1 Y.S. El., R.A.,

(1,090 (1,050 perperp;s.1.) p.s.1.) cent cent 1,100 F., 2 hren...y 700 2134.3 126. 9 26. 0 54. O 16 134. 8 123. 7 k30. 0 68.0 96 137. 2 `128. 027. 0 62. 2 800 l 136. 6 130. 6 28.0 59. 4 16 133. `5 124. 9 29. O 62. 896 131. 4 121. 8 29. O 60. 5 900 42 134. 0 122. 7 29. 0 59.1 16 x 134. 2123. 2 25.0 56. 7 64` 132. 4 124.1 26. 0 58. 5 1, 000 1 133. 9 124. 826. 01 58. 7 6 134. 4 122. 2 27. 0 57. 4 24 134. 5 123. 1 29. 0 59.11,200 F., 2 lirs ,y 700 l2 140.6 134. 3 26. 0 53.1 16 141. 7 138. 2 26.0 59. 8 96 151. 5 144. 0 25. 0 58. 1 v800 l 142.6 137. 7 27. O 55. 4 16154. 8 135. 5 ,27. 0 48. 7 148. 7 134.3 25.0 51. 5 900 2 146. 2 134.9v25. 0 55. 4 16 141. 3 v131.1 25.0. 46. 4 64 137. 3 130.15 24.0 53. 2 1,009 1 139. 0 133. 1 2,4. 0 54. 8 6 130. 3 123. 2 28. 0 56. 4 y 24 132. 2122.9 29. 0 59. 5 `1,300 F., 2 hrs 700 2 199. 6 186.8 1.0 0.8 8 207. 7183. 3 3.0 2. 4 16 207.7 185. 7 3.0 1. 6 V24 207.7 184. 9 4. 0 1. 6 48206. 1 182. 7 2. 0 2. 4 96 20D. 4 178. 8 2. 0 2. 4 800 v1 195. 5 173. 948. 0 7. 9 4 191. 4 161.1 9.9 17.1 8 186. (l 154. 6 13. 0 29. 4 16 182.5 156. 7 16. 0 37.9 48 177. 6 160. 9 ,16. O 42. 2 96 `168. 2 151. 3 18.047. 5 900 l 174. 5 157. 8 15. O` 39. 2 2 ,166. 0 151.4 17.0 48.3 8 158.8 145. 8 18.0 52. 5 16 155. 6 142. 4 21.0 48.1 32 150. 7 141. 4 23. 048. 3 64 145. 0 136. 3 24. 0 57. 0

. up to 3.4.

TABLE II--Contz'nued Tensile Properties Aging Aging Water Quench Temp.,Tune, 5 Time and Temp. F. hrs. Ult. Y.S. El., R.A.,

(1,000 (1,000 per perp.s.i.) p.s.i.) cent cent 1,300 F., 2 hrs.-. 1, 000M 167.2 153.2 21.0 49. 3 162.7 150.5 21.0 49. 5

1 156.4 143. 9 21.0 52. 5 10 2 156. 4 148. 1 22.0 53. 2 6 149. 3 141.523.0 54. 7 24 141.0 135. 2 23. 0 54.1 1,400Q F., 2 hrs... 700 2 16Brittle 96 800 1 215.9 2.0 1.6 15

4 210. 6 1.0 .8 8 214.1 188. 3 5.0 4. 8 16 206. 9 191. 4 10. 0 18.9 48196. 0 177. 0 10.0 26. 7 96 188. 1 175. 4 13. 0 29. 0 900 201. 2 185.17.0 13.1 2 185. 7 171. 5 11.0 34. 8 8 177.2 16a. 9 12.0 24. 5 20 16 168.4 158. 5 15. 0 32.3 32 162. 1 150. 9 18.0 39. l 64 153.0 141.8 25. 0 54.0 1, 000 1/4 182. 6 171. 5 12. 0 27. 3 M 177.8 166. 1 16. 0 48. 7 1172.1 160.9 17. 0 48.1 2 165. 7 153. 5 17.0 43. 8 25 6 153. 5 143. 4 20.0 43. 2 24 146. 6 136. 5 20. 0 43. 4 1,500 F., 2 hrS... 700 1 96 Brittle800 1 4 8 It will be noted that with this alloy, no particular increasein strength, regardless of aging time and temperature, was obtained forspecimens quenched below 1300 F. Specimens quenched from 1300 F. and up,however, are shown to have undergone marked strengthening on subsequentaging. The data also show at a 700 F. aging temperature is too lowforaging to take place in a reasonable time, and that at upwards of 1000F. `the beta-to-alpha transformation occurs too rapidly for convenientcontrol. The best quenched and aged properties are obtained by quenchingin the vicinity of 1400 F., which, for this alloy, is about 150 belowthe beta transus, and thereafter aging at about 800 to 900 F. Tensilestrengths up to 200,000 p.s.i. with elongation are obtainable by thistreatment, as shown by the data. This alloy as quenched in water after 2hours at 14.00 F., had the following properties: ultimate strength177,000 p.s.i., yield strength 171,800 psi., elongation reduction inarea 32.4%.

Various of the Table I1 quenched and aged conditions were alsoinvestigated for notch sensitivity of this alloy. For these tests,standard one-fourth inch notched tensile specimens were employed. Thenotched ultimate vs. plain ultimate ratios observed` on these specimensare given in the following Table III, together With the ultimatestrength and reduction in area for the plain and notched specimens. Thisdata shows that the alloy in the quench-overaged conditon is not notchsensitive at stress concentration TABLE III N otched Tensile Propertieson Heat Treated Ti-6.5 Mn Alloy P.s.i. 1,000 Ult. Red. in Area N. Ult./Condition Strength Percent P. Ult.

Ratio Plain Notched Plain Notched 2hrs. 1,300 F., H2O

Q: +8 hrs. at; 800 F- 186. 0 238. 1 29. 4 5 0 1. 28 2 1,400 F., H2O

+16'hrs. at 800 F-.- 206. 9 249. 0 18. 9 7. 4 1. 21 +2 hrs. at 900 F185. 7 251. 7 34. 8 8. 7 1. 35 +14 hrs. at 900 F.. 168. 4 248. 4 32. 311. 8 1. 49 hr. at 1,000 F 182. 7 252. 4 27. 3 5. 3 1. 33 hr. ai; 1,000F 177. 8 248. 2 48. 7 8. 1 1. 40 2 hrcsi 1,500 F., H2O

+8 hrs. at 900 F 202. 5 230. 0 6. 4 7. 8 1. 13 +16 hrs. at 900 F 190. 7235. 9 13. 1 8. 7 1. 23 +32 hrs. at 900 F- 180. 2 227. 2 13. 8 8. 3 1.26

Table IV below gives the results of a series of quenching and agingtests on a mixed phase, alpha-beta alloy containing about 4% aluminum,4% manganese and the balance titanium of commercial purity. These testswere conducted in the same manner as those for the above Table Il. Thebeta transus temperature for this alloy is about 1700 F.

TABLE 1V Quenched and Aged Tensile Properties of 'l`l-4Al-4Mn AlloyTensile Properties Aging Aging Water Queneh Temp., Time, Time and Temp.F. hrs. Ult. Y.S. El., RA.,

(1,000 (1,000 perperp.s.1.) p.s.i.) i cent cent 1,350 F., 2 hrs. 157. 6148. 4 18. 0 42.0 700 2 158. 7 148. 7 20. 0 46. 5 16 162. 9 151. 7 16. 040. 9 48 167. 7 153. 8 12. 0 36. 2 800 2 160. 9 148. 4 17. 0 44.0 16188. 2 157. 1 7. 0 9. 3 48 189. 8 165.8 13. 0 27. 5 900 l 163. 5 151. 415. 0 42. 9 16 183. 3 162. 3 13.0 31. 4 24 182.1 164. 4 14. 0 30.1 1,000 2 165.6 150.8 13. 0 30. 2 16 161. 3 148. 6 15.0 39. 7 24 161. 5 151.4 18.0 38. 7 1,450 F., 2 hrs 150.1 149.1 21.0 42. 5 700 2 178. 6 160. 313.0 14.8 15 215. 9 171.7 4. 0 4.1 24 205. 7 168. 5 2.0 1. 6 48 167. 7153.8 12. 0 36. 2 S00 2 213.8 170. 5 6. 0 10.2 8 220. 1 178.8 5. 0 3. 924 202. 9 170.3 9. 0 20. 5 48 215.9 177.4 5. 0 10.2 900 2 205.3 173. 28.0 24.0 4 211.8 172.1 5. 0 13. 2 24 200. 8 176. 0 10.0 24. 8 1, 000 1186. 3 169. 9 11. 0 30. 2 2 184. 8 162.8 11.0 30. 2 15 167.3 152. 5 14.0 38. 1 24 169. 5 154. 3 15.0 38.4 1,550 F., 2 11113...- 156. 9 150.517.0 36. 8

It will be seen from Table IV that the quenching and aging response ofthis Ti-4Al-4Mn alloy is gener-ally similar to that of the Ti-6.5Mnalloy of Table Il', except that optimum properties are in this instanceobtained by quenching from about 1353-1450" F. and aging at about900-1000 F. Here again, tensile strengths up to about 200,000 p.s.i.with accompanying elongation of about are obtained.

Referring now to the annexed drawings for a further description oftheinvention:

FIGS. l to 5, inc., are photomicrographs showing the microstructure of aTi-7Ivin, mixed phase, alpha-beta aiioy after being subjected to variousheat treatments according to the invention as discussed below.

FIG. 6 is a graph comparing the strength versus ductility of the'I`i-7Mnl alloy as quenched from the alphabeta field and also aftersubsequent aging.

FIG. 7 is a plot of tensile vstrength versus ductility of numerousspecic analyses lof mixed phase, alpha-beta alloys, as quenched fromabove the beta transus temperature; while FIG. 8 is a comparative plotof such alloys as quenched from below the beta transus temperature.

FIG. 9 isa plot showing the beta transus temperature versus alloycontent for various binary alloys of titanium and a betastabilizingelement.

Referring to the photomicrographs FIGS. 1 to 3, inc., show as quenchedmicrostructures of the Ti-7Mn alloy as water quenched from 1375, l1425and 1575 F., respectively. As shown by FiG. 9, the beta transustemperature of this alloy is about 780 C. or l440 F. Thus FIGS. 1 and 2show the alloy asquenched from the alpha-beta field and FIG. 3 asquenched from theV beta field. It will be noted that increasingquenching ltemperature results in decreasing amounts of alpha titanium(darker etching islands) in the beta titanium matrix (light background).This, as shown in the drawing, is accompanied by increasing tensilestrength with decreasing ductility and increasing hardness, as measuredon the Rockwell A scale and designated RA. t will further be noted thatwhereas quenching from the alpha-beta iield gives combinationsof highstrength and ductility, quenching from the beta iield rendered the alloyglass brittle.

FIGS. 4 and 5 illustrate the aging response pattern of i specimens ofthe alloy as air cooled in one instance from l425 F. and aged 4 hours at600 F., FIG. 4, and as air cooled from 1425 F. in the other instance andaged 4 hours at `800" F., FIG. 5. Note that the FiG. 4 structure isglass brittle and quite hard, RA 73.6. This material has been aged butnot overaged. The structure of FIG. 5, on the other hand, has been agedat a higher temperature and is in the overaging condition as indicatedby the dark etching background. The dark etching background is theresult of a very fine dispersion of transformed alpha titanium in thebeta titanium matrix, the white etching islands being the alpha titaniumpresent prior to aging.

As a result of this overaging, it will be noted that the FIG. 5structure has regained considerable ductility and is much softer thanthe FIG. 4 structure.

Referringto FIG.` 6, the solid dots are plots of ultimate strengthversus tensile elongation for quenched specimens of the Ti-7Mn alloy asquenched'from various temperatures in the alpha-beta field; while thecircles are similar plots of this alloy as quenched from variousalpha-beta field temperatures and subsequently aged at varyingtemperatures and times. The purpose of the plot is to show that the asquenched mechanical properties can be duplicated in the quenched andaged specimensas regards any desired combination of strength andductility. This is of prime importance because, as shown above, thedistribution of the alpha and beta phases in the ailoy as quenched fromthe alpha-beta iield, is ideal as regards strength and ductility. Hencethe ability to duplicate these as quenched properties in the alloys asquenched and aged, results in the attainment of maximumstrength-ductility combinations combined with. high thermal'l stability.

As shown above in Table I for various typical mixed alpha-beta alloys,quenching from the beta field in general renders the alloys weak andbrittle; whereas quenching `from the alpha-beta field results in generalin greatly iucreased strength with retention of good ductility. Thatthese observations are rules of general application is shown by the testresults plotted in FIGS. 7 and 8.

In FIG. 7 is plotted ultimate strengths versus percent tensileelongations for numerous mixed alpha-beta alloys as heat treated in thebeta field and quenched. Test results are given for such alloyscontaining about 2 to 15 atomic percent of one `or more of M0, Mn, Cr,Fe. FIG. 8 is a similar plot of such alloys as heat treated in thealpha-beta iield and quenched.

It will be seen from the envelope curves A, FIG. 7, and B-B, FIG. 8,that for any given ductility, the strength level is much higher forthese alloys as heat treated in the alpha-beta field than when treatedin the beta eld. Based on Adata similar to FIGS. 7 and 8 for the Ti-7Mriand Ti-4Al-4Mn alloys, the advantage of heat treating in the alpha-betafield as compared to heat treating in the beta iield prior to aging oroveraging is shown by the following:

Attaiu able Vattainable Ductility Ductility Strength Level Alpha-Betatized,

' percent It will be seen from the above data that at any given strengthlevel, greater ductility is secured by heat treating the alloy in thealpha-beta eld in accordance with the present invention, i.e., byquenching from below the beta transus temperature followed 'by aging,than is -obtainable by quenching from above the beta transus temperaturefollowed by aging.

Although best results are generally obtainable by rapid quenching of thealloys from below the beta Vtransus temperature, as by quenching intowater, other quenching media may be employed such asoil quenching andeven cooling in air, the latter as shown by some of the examples abovediscussed.

Referring to FIG. 9 there is shown a plot of the beta transustemperature Versus alloy content for titanium binary alloys containing,respectively, the beta promoter additions chromium, vanadium, manganese,iron and molybdenum. Corresponding plots for other beta prornoteradditions have been published in the literature. The beta transustemperature for any particular alloy may be determined by quenchingspecimens from progressively higher temperatures, until a completelymartensitic or retained beta microstructure is obtained.

The heat treatment process of the invention is applicable in general totitanium base alloys having a mixed alpha-beta microstructure. Suchalloys are generally those containing about 2 to 15 atomic percent ofone or more beta promoters. In such alloys the isomorphous betapromoters, molybdenum, vanadium, columbium and tantalum may be presentsingly or in aggregate up to the upper limit of about 15 atomic percent.The same is also true of the sluggishly eutectoid beta promoterschromium and tungsten. Manganese may be present up to about 10 percentby Weight and iron up to about 7 percent by weight, consistent with theretention of adequate ductility in the alloy. The rapidly eutectoid betapromoters cobalt, nickel and copper may be present up to about 5 percentby weight singly or in aggregate. For all such additions, the lowereiiective limit is about 0.5% and preferably about 1% by Weight.

The mixed phase alloys to which the invention is applicable may alsocontain one or more of the alpha promoters, the more important of whichare, aluminum up to about 8 percent by weight, tin up to about 23percent by Weight, and antimony up to about 18 percent by Weight, yforthe ductile alloy range. Here again, the lower ellective limit for theseadditions is about 0.5 percent and preferably about 1 percent by weightsingly or in aggregate.

The interstitials carbon, oxygen and nitrogen, which also function asalpha promoters, should not be present in these alloys in amountexceeding about 0.2 percent each by Weight.

It was pointed out at the outset that for securing a good alpha-betadistributon, plastic deformation in the alpha-beta eld cannot always beresorted to, as for example in the case of massive forgings, and that insuch cases the distribution is alternatively obtained by slow coolingifrom above the beta transus temperature, an appropriate cooling ratebeing about 250 F. per hour.

Even in the case of products formed of rolled sheet or rod or drawnWire, which as rolled and/ or drawn in the alpha-beta temperature range,has a good alpha-beta distribution, it is frequently not possible to usethe material in the as rolled or drawn conditions, `owing to fabricationoperations to which this semi-finished product must, in many instances,be subjected, such, for example, as blanking, punching and formingoperations. It is often necessary that such rolled or drawn materialhave considerably lower properties for these operations than arerequired in the finished articles. The material must, therefore, beconverted to the annealed condition for the iinal finishing operationsas by slow cooling from the beta field, in which case it must thereafterbe hardened and strengthened, this being accomplished by quenching frombelow the beta transus temperature and subsequently aging in accordancewith the heat treatment of the invention herein.

What is claimed is:

1. A Wrought and age hardened titanium base alloy containing about: 2-15atomic percent of at least one element which stabilizes the beta phaseat atmospheric temperatures, up to 23% by Weight of at least one elementwhich stabilizes the alpha phase at atmospheric tempera l0 tures, and upto 0.2%, each of carbon, oxygen and nitrogen balance titanium,characterized by a microstructure consisting of a beta matrix containinga dispersion of alpha and transformed alpha particles, and by anultimate strength of at least 160,000 p.s.i. and a tensile elongation ofat least 5%.

2. A wrought and age hardened titanium base alloy containing about: 2-15atomic percent of at least one element which stabilizes the beta phaseat atmospheric tem peratures, up to 23% by weight of at least oneelement which stabilizes the alpha phase at atmospheric temperatures,and up to 0.2% each of carbon, oxygen and nitrogen balance titanium,characterized by a microstructure consisting of a beta matrix containinga dispersion of a1- pha and transformed alpha particles, and by anultimate strength of at least 180,000 p.s.i. and a tensile elongation ofat least 5%.

3. A wrought and age hardened titanium base alloy containing about: 215atomic percent of at least one element which stabilizes the beta phaseat atmospheric temperatures, 0.5 to 23% by Weight of an alphastabilizing metal selected from the group consisting of tin and aluminumand mixtures thereof, but not to exceed 8% aluminum, and up to 0.2% eachof carbon, oxygen and nitrogen balance titanium, characterized by amicrostructure consisting of a beta matrix containing a dispersion ofalpha and transformed alpha particles, and by an ultimate strength of atleast 180,000 p.s.i. and a tensile elongation of at least 5%.

4. A Wrought and age hardened titanium base alloy containing about: 2-15atomic percent of a beta promoting metal selected from the groupconsisting of vanadium, molybdenum, columbium, tantalum, chromium,tungsten, manganese and iron, and mixtures thereof', but not to exceed10% by weight of manganese and 7% by Weight of iron, up to 23% by Weightof alpha promoting elements, but not to exceed 8% by weight of aluminumand 18% by Weight of antimony when present, and up to 0.2% each ofcarbon, oxygen and nitrogen balance titanium, characterized by amicrostructure compri-sing a fine dispersion of transformed alphatitanium in a beta matrix, together with islands of alpha titanium, andfurther characterized by an ultimate strength of at least 180,000 p.s.i.and a tensile elongation or at least 5%.

5. A wrought and age hardened titanium base alloy containing about: 2-15atomic percent of at least one beta promoting element selected from thegroup consisting of Vanadium, molybdenum, columbium, tantalum, chromium,tungsten, manganese and iron, but not to exceed 10% by Weight ofmanganese and 7% by weight of iron, 0.5 to 23% by Weight of alphapromoting elements, but not to exceed 8% by weight of aluminum and 18%by Weight of antimony when present, and up to 0.2% each of carbon,oxygen and nitrogen balance titanium, characterized by a microstructurecomprising a tine dispersion of transformed alpha titanium in a betamatrix, together with islands of alpha titanium, and furthercharacterized by an ultimate strength of at least 180,000 p.s.i. and atensile elongation of at least 5 References Cited in the file of thispatent UNITED STATES PATENTS 2,821,475 AJaffee et al. k Jan. 28, 1958UNITED STATES PATENT OFFICE CERTIFICATE OE CORRECTION Patent Noo 3q 151i0035 September 29i7 1964 Milton B, Vordahl It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as Corrected below.

Column 1, line 22l May 317 1951 (now Column 5V line 50l for "at" readColumn 6i TABLE IVg under the column heading "U1t (1,000 p.,s.,i)"L line14 thereon for. "'1501' read 1561 column 7v same TABLE IVY line 4thereofY for 1959" seme Column heedinhz 34, for V'distlf'ibuton read1959 --3 column 9u line read distribution --0 Signed and sealed this30th day of March 1965o (SEAL) Attest:

ERNEST W. SWIDERl EDWARD J. BRENNER Attesting Officer Commissioner ofPatents

1. A WROUGHT AND AGE HARDENED TITANIUM BASE ALLOY CONTAINING ABOUT 2-15ATOMIC PERCENT OF AT LEAST ONE ELEMENT WHICH STABILIZES THE BETA PHASTAT ATMOSPHERIC TEMPERATURES, UP TO 23% BY WEIGHT OF AT LEAST ONE ELEMENTWHICH STABILIZES THE ALPHA PHASE AT ATMOSPHERIC TEMPERATURES, AND UP TO0.2%, EACH OF CARBON, OXYGEN AND NITROGEN BALANCE TITANIUM,CHARACTERIZED BY A MICROSTRUCTURE CONSISTING OF A BETA MATRIX CONTAININGA DISPERSION OF ALPHA AND TRANSFORMED ALPHA PARTICLES, AND BY ANULTIMATE STRENGTH OF AT LEAST 160,000 P.S.I. AND A TENSILE ELONGATION OFAT LEAST 5%.